The field of the invention is heavy equipment used for collecting and moving a load from one place to another, and for measuring the weight of the load while it is being moved.
More particularly, the field of the invention is heavy equipment for surface mining loading operations such as power shovels, drag lines, and the like, and more particularly, systems used on such equipment to measure the net weight of material in each load.
In large scale surface mining operations, equipment of immense proportions is used to load and transport material. Loading is usually performed by power shovels with a dipper capacity of about 100 tons per scoop. Equally mammoth trucks are loaded with the material and haul it to a processing location. The largest trucks have a capacity of about 360 tons.
Overloading the trucks can lead to premature fatigue and failure causing excessive maintenance costs. Without a measurement of the actual weight of material in the truck, the power shovel operator can only guess the weight based on an extremely rough estimate of the volume of material in the truck. Therefore, to prevent chronic overloading, the trucks are routinely underloaded. But such underloading can cause significant loss of production.
Measurement systems have been developed to indicate the net weight of material in the power shovel dipper as it is transferred to the truck. The prior measurement systems function by first sensing the electrical load of the power shovel drive motors, then computing the motor dynamics based on that electrical load, and finally computing an estimate of the net weight based on the motor dynamics, the known power shovel geometry, and the known tare weights. Examples of such known systems include Radomilovich U.S. Pat. No. 4,677,599 and Blair et al. U.S. Pat. No. 4,809,794, which averages stored weight determinations calculate an actual material weight.
Although such measurement systems have been constructed and used, they have been ineffective due to large inaccuracies in the measurements on the order of .+-.20% or more. These errors stem from the fact that the existing measurement systems do not effectively account for the complex dynamic operation of such enormous equipment, or for all the environmental effects on the equipment, such as the level of the mine surface where the shovel is located. Therefore, measurements are not only in error, but are erratic and unpredictable. In order to be effective, a measurement system has to be capable of accurately and repeatedly performing measurements to within a small error, say .+-.2% for example. Otherwise, the problems of overloading and underloading would persist. Although the above noted measurement systems have attempted to account for dynamic factors affecting the load weighing process, such systems have been either too complex or incomplete.